Heat recovery system

ABSTRACT

A heat recovery system includes a first air cooler for cooling compressed air from a compressor, a first oil cooler for cooling a lubricant from the compressor, and a second air cooler and/or a second oil cooler serving as a heat recovering heat exchanger. The second air cooler heats water with the heat of the compressed air to be fed to the first air cooler. In contrast, the second oil cooler heats water with the heat of a lubricant to be fed to the first oil cooler.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-234271 filed Oct. 19, 2010. The content of the application is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat recovery system for recovering heat of compression in an air compressor.

2. Description of the Related Art

There has been known a heat recovery system in which compressed air or a lubricant from a compressor is cooled by using feedwater to a feedwater tank in a boiler, and further, the feedwater to the feedwater tank is heated. Specifically, water is supplied to the feedwater tank in the boiler via an air cooler and an oil cooler, and then, the compressed air is cooled in the air cooler whereas the lubricant from the compressor is cooled in the oil cooler, wherein both of the coolers heat the feedwater to the feedwater tank.

Here, cooling types of a compressor include a water cooling type and an air cooling type. In the case of the water cooling type, an air cooler and an oil cooler in a compressor unit circulate water to and from a water cooler such as a cooling tower. The water passing through the air cooler and the oil cooler is cooled in the water cooler, to be then recycled. The circulation of the cooling water is replaced with a technique for producing hot water.

However, the heat recovery system according to the above-described technique includes merely one air cooler and one oil cooler. That is to say, heat is recovered by using the air cooler and the oil cooler which should be originally provided for a compressor unit. The amount of water passing through each of the coolers is adjusted in such a manner that the temperature of the compressed air passing through the air cooler or the temperature of the lubricant passing through the oil cooler is kept at a desired value based on the temperature.

Consequently, in the water cooling type compressor, no cooling water is circulated between the air cooler and the oil cooler, and the water cooler such as the cooling tower, and further, in the air cooling type compressor, neither the compressed air nor the lubricant are cooled by causing outside air to pass through the air cooler and the oil cooler. Thus, no existing cooling system originally provided for the compressor remains.

In addition, it is impossible to adjust the feedwater or its amount according to a use load (i.e., required amount) of hot water obtained by causing the air to pass through each of the coolers. For example, even in the case of no or little use of the hot water or stoppage of production of the hot water, the stoppage of production of the hot water signifies the stoppage of supply of cooling water to each of the coolers, thereby making it impossible to cool the compressed air and the lubricant. Thus, the hot water cannot be produced according to the use load of the hot water.

Moreover, the amount of feedwater to each of the coolers is adjusted in such a manner as to keep the compressed air or the lubricant at the desired temperature, but the feedwater to each of the coolers or its amount is not adjusted in such a manner as to keep the hot water obtained by causing the water to pass through each of the coolers at the desired temperature. In other words, the hot water having the desired temperature cannot be obtained.

A problem to be solved by the present invention is to provide a heat recovery system capable of recovering the heat of compression while an existing compressor cooling system remains as it is. Preferably, a problem to be solved by the present invention is to provide a heat recovery system which can be operated according to a use load of hot water or operated in such a manner as to obtain the hot water at a desired temperature.

SUMMARY OF THE INVENTION

The present invention has been accomplished to solve the problems to be solved. The invention of a first aspect is directed to a heat recovery system including: a first air cooler for cooling compressed air from a compressor; a first oil cooler for cooling a lubricant from the compressor; and a second oil cooler which is disposed on an oil feed path to the first oil cooler and serves as a heat recovering heat exchanger for heating water with the heat of the lubricant to be fed to the first oil cooler.

According to the invention of the first aspect, the heat recovery system includes the second oil cooler in addition to the first air cooler and the first oil cooler, and therefore, the heat of compression can be recovered in the second oil cooler. At this time, the first air cooler and the first oil cooler are used as an existing compressor cooling system while the heat of compression can be recovered in the second oil cooler. Moreover, even if feedwater to the second oil cooler or its amount is adjusted according to a use load of hot water or the like, no influence is exerted on required cooling of the compressed air or the lubricant in the first air cooler and the first oil cooler.

The invention of a second aspect is directed to the heat recovery system according to the first aspect, further including a second air cooler in addition to the second oil cooler, wherein the second air cooler is disposed on an air feed path to the first air cooler and serves as a heat recovering heat exchanger for heating water with the heat of the compressed air to be fed to the first air cooler, the second air cooler and the second oil cooler being disposed in such a manner as to allow the water to pass therethrough in series or parallel.

According to the invention of the second aspect, the heat recovery system includes the second air cooler and the second oil cooler in addition to the first air cooler and the first oil cooler, and therefore the heat of compression can be recovered in the second air cooler and the second oil cooler. At this time, the first air cooler and the first oil cooler are used as an existing compressor cooling system while the heat of compression can be recovered in the second air cooler and the second oil cooler. Moreover, even if feedwater to the second air cooler and the second oil cooler or its amount is adjusted according to a use load of hot water or the like, no influence is exerted on required cooling of the compressed air or the lubricant in the first air cooler and the first oil cooler.

The invention of a third aspect is directed to the heat recovery system according to the first aspect, further including a second air cooler in place of the second oil cooler, wherein the second air cooler is disposed on an air feed path to the first air cooler and serves as a heat recovering heat exchanger for heating water with the heat of the compressed air to be fed to the first air cooler.

According to the invention of the third aspect, the heat recovery system includes the second air cooler in addition to the first air cooler and the first oil cooler, and therefore, the heat of compression can be recovered in the second air cooler. At this time, the first air cooler and the first oil cooler are used as an existing compressor cooling system while the heat of compression can be recovered in the second air cooler. Moreover, even if feedwater to the second air cooler or its amount is adjusted according to a use load of hot water or the like, no influence is exerted on required cooling of the compressed air or the lubricant in the first air cooler and the first oil cooler.

The invention of a fourth aspect is directed to the heat recovery system according to any one of the first to third aspects, wherein feedwater to the heat recovering heat exchanger or its amount is controlled based on a use load of hot water after passing through the heat recovering heat exchanger.

According to the invention of the fourth aspect, feedwater is controlled based on a use load of hot water, thus producing the desired hot water. Even if the feedwater is controlled based on the use load of the hot water, the first air cooler can securely cool the compressed air, and further, the first oil cooler can securely cool the lubricant.

The invention of a fifth aspect is directed to the heat recovery system according to any one of the first to third aspect, wherein feedwater to the heat recovering heat exchanger or its amount is controlled based on the temperature of hot water after passing through the heat recovering heat exchanger.

According to the invention of the fifth aspect, the feedwater is controlled based on the temperature of the hot water, thus producing the desired hot water. Even if the feedwater is controlled based on the temperature of the hot water, the first air cooler can securely cool the compressed air, and further, the first oil cooler can securely cool the lubricant.

The invention of a sixth aspect is directed to the heat recovery system according to any one of the first to third aspects, wherein the compressor is of an oil lubrication type, and includes an oil separator for separating the lubricant from the compressed air discharged from the compressor; and the compressed air, from which the lubricant is separated in the oil separator, is fed to each of the air coolers whereas the lubricant from the oil separator is fed to each of the oil coolers.

According to the invention of the sixth aspect, the similar functions and effects as those produced by the invention according to any one of the first to third aspects can be produced even in the compressor of the oil lubrication type.

The invention of a seventh aspect is directed to the heat recovery system according to any one of the first to third aspects, wherein the compressor is of a non-lubrication type including a low stage compressor and a high stage compressor, the compressed air from the low stage compressor being fed to the high stage compressor through a first inter cooler and further compressed in the high stage compressor, before being fed to each of the air coolers as after coolers, and the compressor further includes a second inter cooler which is disposed on an air feed path to the first inter cooler from the low stage compressor and serves as the heat recovering heat exchanger for heating the water with the heat of the compressed air to be fed to the first inter cooler.

According to the invention of the seventh aspect, the similar functions and effects as those produced by the invention according to any one of the first to third aspects can be produced even in the compressor of the non-lubrication type.

The invention of an eighth aspect is directed to the heat recovery system according to the seventh aspect, wherein the water is heated to produce steam in the heat recovering heat exchanger, and feedwater to the heat recovering heat exchanger or its amount is controlled based on the water level of the heat recovering heat exchanger.

According to the invention of the eighth aspect, the heat of compression in the air compressor is recovered, thus producing the steam.

The invention of a ninth aspect is directed to the heat recovery system according to any one of the first to third aspects, wherein the compressor is of a water lubrication type, lubricating water being used in place of the lubricant, and accordingly, the first oil cooler being replaced with a first water cooler for cooling the lubricating water whereas the second oil cooler being replaced with a second water cooler serving as a heat recovering heat exchanger for heating water with the heat of the lubricating water to be fed to the first water cooler; and the compressor includes a separator for separating the lubricating water from the compressed air discharged from the compressor; and no first air cooler is disposed, whereby the compressed air from the compressor is discharged via the separator.

According to the invention of the ninth aspect, the similar functions and effects as those produced by the invention according to any one of the first to third aspects can be produced even in the compressor of the water lubrication type.

The present invention can implement the heat recovery system in which the existing compressor cooling system remains as it is while the heat of compression can be recovered. In the preferred embodiments, the heat recovery system can be operated according to the use load of the hot water or can be operated in such a manner as to obtain the hot water at a desired temperature. Hence, even if the amount or temperature of the hot water obtained is adjusted, the system cannot influence the cooling operation in the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing a heat recovery system in a first preferred embodiment according to the present invention;

FIG. 2 is a view schematically showing a heat recovery system in a second preferred embodiment according to the present invention;

FIG. 3 is a view schematically showing a heat recovery system in a third preferred embodiment according to the present invention and showing only differences from the first and second preferred embodiments; and

FIG. 4 is a view schematically showing a heat recovery system in a fourth preferred embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A detailed description will be given below of preferred embodiments according to the present invention with reference to the attached drawings.

First Preferred Embodiment

FIG. 1 is a view schematically showing a heat recovery system in a first preferred embodiment according to the present invention.

A heat recovery system 1 in the present preferred embodiment is a system for recovering the heat of compression in an oil lubrication type (oil supply type) and water cooling type motor air compressor. Specifically, the heat recovery system 1 is adapted to cool compressed air or a lubricant and heat feedwater to a feedwater tank 5 by indirectly exchanging heat between the compressed air or the lubricant from a compressor 2 and feedwater from a water softener 3 to the feedwater tank 5 in a boiler 4.

The heat recovery system 1 in the present preferred embodiment includes, as essential components; the compressor 2 for taking in, compressing, and discharging outside air; a motor 6 for driving the compressor 2; an oil separator 7 for separating the lubricant from the compressed air; a first air cooler 8 and a second air cooler 9 for cooling the compressed air; and a first oil cooler 10 and a second oil cooler 11 for cooling the lubricant.

The compressor 2 is driven by the motor 6, to take in, compress, and discharge the outside air. The compressed air discharged from the compressor 2 is fed to the oil separator 7, where the lubricant is separated and removed.

The compressed air, from which the lubricant is removed in the oil separator 7, has been fed to compressed air utilizing equipment, not shown, via the first air cooler 8 in the conventionally known compressor unit. However, in the present preferred embodiment, the compressed air is fed to the compressed air utilizing equipment via the second air cooler 9 and the first air cooler 8. In the present preferred embodiment, the second air cooler 9 is disposed on an air feed path 12 from the oil separator 7 to the first air cooler 8, and therefore, the compressed air from the oil separator 7 is fed to the compressed air utilizing equipment via the second air cooler 9 and the first air cooler 8. Incidentally, a dryer 13 may be installed, as desired, on an outlet side of the first air cooler 8, and thus, moisture contained in the compressed air is removed by the dryer 13, to be thus fed to the compressed air utilizing equipment.

In the meantime, the lubricant in the compressor 2 has been returned to the compressor 2 via the first oil cooler 10 in the conventionally known compressor unit. In contrast, in the present preferred embodiment, the lubricant is returned to the compressor 2 via the second oil cooler 11 and the first oil cooler 10. Specifically, in the present preferred embodiment, the second oil cooler is disposed on an oil feed path 14 from the oil separator 7 to the first oil cooler 10, so that the lubricant is returned from the oil separator 7 to the compressor 2 via the second oil cooler 11 and the first oil cooler 10.

The oil feed path from the oil separator 7 to the second oil cooler 11 and another oil feed path from the first oil cooler 10 to the compressor 2 are connected to each other on a bypass 15. Moreover, a temperature adjusting three-way valve 16 is disposed at a branch portion between the oil feed path from the oil separator 7 to the second oil cooler 11 and the bypass 15. A wax type of temperature adjusting three-way valve 16 should be preferably used. The temperature adjusting three-way valve 16 adjusts a distribution rate under its own power based on the temperature of the lubricant from the oil separator 7 so as to feed the lubricant to each of the oil coolers 11 and 10 or to return the lubricant to the compressor 2 via not each of the oil coolers 11 and 10 but the bypass 15. In this manner, it is possible to adjust the flow rate of the lubricant passing through each of the oil coolers 11 and 10, to thus keep the lubricant inside of the compressor 2 at a desired temperature.

Hereinafter, the coolers 8 to 11 will be explained in order. First, the first air cooler 8 is an indirect heat exchanger between the compressed air and its cooling water. Moreover, the second air cooler 9 is an indirect heat exchanger between the compressed air and the feedwater to the feedwater tank 5.

In the meantime, the first oil cooler 10 is an indirect heat exchanger for the lubricant in the compressor 2 and its cooling water. Moreover, the second oil cooler 11 is an indirect heat exchanger for the lubricant in the compressor 2 and the feedwater to the feedwater tank 5.

In the present preferred embodiment, the cooling water is allowed to pass through the first air cooler 8 and the first oil cooler 10, to be then circulated between the coolers and a water cooler 17 such as a cooling tower. Specifically, the water cooler 17 cools the cooling water passing through the first air cooler 8 and the first oil cooler 10, and circulates the cooling water between the coolers 8 and 10.

As a box indicated by a chain double-dashed line, the compressor 2, the motor 6, the oil separator 7, the first air cooler 8, and the first oil cooler 10 may be constituted as a compressor unit 18. In this case, the compressor unit 18 may be a conventionally known compressor unit (including an existing compressor unit). The second air cooler 9 is disposed on the air feed path 12 from the compressor 2 (more particularly, the oil separator 7) to the first air cooler 8, and further, the second oil cooler 11 is disposed on the oil feed path 14 from the compressor 2 (more particularly, the oil separator 7) to the first oil cooler 10, thus constituting the heat recovery system 1 in the present preferred embodiment. Here, the dryer 13 may be housed inside of the compressor unit 18.

Next, explanation will be made on a feedwater system to the boiler 4. In the present preferred embodiment, water (i.e., soft water) passes through the second air cooler 9 and the second oil cooler 11 in order from the water softener 3, and then, is discharged to the feedwater tank 5. The water in the feedwater tank 5 is appropriately supplied to the boiler 4 via a check valve 20 by a feedwater pump 19. Steam is generated by heating the water in the boiler 4, to be then fed to steam use facility, not shown. The water is fed from the water softener 3 to the feedwater tank 5 via the second air cooler 9 and the second oil cooler 11. Alternatively, the water may be directly fed not via the coolers 9 and 11.

In the heat recovery system 1 in the present preferred embodiment, the second air cooler 9 and the second oil cooler 11 function as a heat recovering heat exchanger for recovering the heat of compression so as to produce hot water. That is to say, the feedwater to the feedwater tank 5 is thermally exchanged with the compressed air in the second air cooler 9, and then, is heated, and further, it is thermally exchanged with the lubricant from the compressor 2 in the second oil cooler 11, and then, is heated, and further, is supplied to the feedwater tank 5 as the hot water.

In the heat recovery system 1 in the present preferred embodiment, the feedwater to the second air cooler 9 and the second oil cooler 11 or its amount is controlled based on a use load of the hot water after passing through the coolers 9 and 11. In place of or in addition to this, the feedwater to the second air cooler 9 and the second oil cooler 11 or its amount is controlled based on the temperature of the hot water after passing through the coolers 9 and 11.

More specifically, a water level sensor 21 is disposed in the feedwater tank 5. Examples of the water level sensor 21 include an electrode type water level detector, an electrostatic type water level detector, float type water level detector, and the like. Opening/closure or opening degree of a feedwater valve 23 disposed on a water feed path 22 to the feedwater tank 5 is changed in response to a signal detected by the water level sensor 21. For example, when the water level inside of the feedwater tank 5 is higher than an upper limit water level at no or few use load of the hot water, the feedwater valve 23 is closed. Thereafter, when the water level inside of the feedwater tank 5 is lower than a lower limit water level, the feedwater valve 23 is opened. Alternatively, the opening degree of the feedwater valve 23 may be adjusted such that the water level inside of the feedwater tank 5 becomes a set water level.

In place of or in addition to the control based on the use load of the hot water described above, the feedwater to the feedwater tank 5 or its amount may be controlled based on the temperature of the hot water. In this case, a temperature sensor 24 is disposed on the water feed path or the feedwater tank 5 after the water passes through both of the coolers 9 and 11. Opening/closure or opening degree of the feedwater valve 23 disposed on the water feed path 22 to the feedwater tank 5 is changed in response to a signal detected by the temperature sensor 24. For example, the opening degree of the feedwater valve 23 may be adjusted such that the temperature detected by the temperature sensor 24 is kept at a set value. During this control, the water level sensor 21 monitors the water level inside of the feedwater tank 5. When the water level is higher than the set water level, it may be determined that the production of the hot water is unnecessary, so as to close the feedwater valve 23. Even if the feedwater is stopped to the second air cooler 9 and the second oil cooler 11, the compressed air and the lubricant can be desirably cooled in the first air cooler 8 and the first oil cooler 10, as described above.

Incidentally, although in either case, the feedwater valve 23 may be disposed on an outlet side of both of the second air cooler 9 and the second oil cooler 11, the feedwater valve 23 should be preferably disposed on an inlet side of both of the second air cooler 9 and the second oil cooler 11, like the preferred embodiment shown in the drawings, in consideration of influences by a water pressure exerted on the second air cooler 9 and the second oil cooler 11 or the temperature.

As described above, the heat recovery system 1 in the present preferred embodiment includes the second air cooler 9 and the second oil cooler 11 in addition to the first air cooler 8 and the first oil cooler 10. Even in the state in which the feedwater is stopped to the feedwater tank 5 via the second air cooler 9 and the second oil cooler 11, requested cooling can be achieved in the first air cooler 8 and the first oil cooler 10. Typically, the first air cooler 8 and the first oil cooler 10 are used as the existing compressor cooling system while the second air cooler 9 and the second oil cooler 11 are disposed.

In the heat recovery system 1 in the present preferred embodiment, the heat of compression can be recovered to produce the hot water in the second air cooler 9 and the second oil cooler 11. Moreover, the hot water can be produced according to the use load of the hot water or the hot water can be produced at a desired temperature. In addition, even if the feedwater to the second air cooler 9 and the second oil cooler 11 or its amount is adjusted, the adjustment cannot influence the requested cooling of the compressed air or the lubricant in the first air cooler 8 and the first oil cooler 10. In other words, even if the feedwater passing through the second air cooler 9 and the second oil cooler 11 or its amount is adjusted, the temperature of the compressed air or the lubricant can be decreased down to the target value or lower in the first air cooler 8 and the first oil cooler 10.

Second Preferred Embodiment

FIG. 2 is a view schematically showing a heat recovery system 1 in a second preferred embodiment according to the present invention.

The heat recovery system 1 in the second preferred embodiment also is basically similar to the heat recovery system 1 in the first preferred embodiment. Hence, a description will be mainly given of differences between the first and second preferred embodiments. The same component parts are designated by the same reference numerals.

In the first preferred embodiment, all of the compressed air from the compressor 2 is fed to the first air cooler 8 via the second air cooler 9. In contrast, in the second preferred embodiment, the second air cooler 9 can be switched or the distribution rate can be changed by switching the second air cooler 9. For the purpose of this, a bypass air feed path 25 connects the inlet and outlet of the second air cooler 9 to each other, and further, a three-way valve 26 is disposed at a branch portion between the air feed path 12 to the second air cooler 9 and the bypass air feed path 25. In place of the three-way valve 26, a solenoid valve or a motor-operated valve may be disposed on the air feed path 12 from the branch portion to the second air cooler 9 or the bypass air feed path 25. At any rate, in the present preferred embodiment, when the compressed air from the compressor 2 is fed to the first air cooler 8, the switch of the second air cooler 9 or its distribution rate can be adjusted.

Although all of the lubricant in the compressor 2 is fed to the first oil cooler 10 via the second oil cooler 11 in the first preferred embodiment, the switch of the second oil cooler 11 or its distribution rate can be changed in the second preferred embodiment. Therefore, a bypass oil feed path 27 connects the inlet and outlet of the second oil cooler 11, and further, a three-way valve 28 is disposed at the branch portion between the oil feed path 14 to the second oil cooler 11 and the bypass oil feed path 27. In place of the three-way valve 28, a solenoid valve or a motor-operated valve may be disposed on the oil feed path 14 from the branch portion to the second oil cooler 11 or the bypass oil feed path 27. At any rate, in the present preferred embodiment, when the lubricant from the compressor 2 is fed to the first oil cooler 10, the switch of the second oil cooler 11 or its distribution rate can be adjusted. The other constitution and control are similar to those in the first preferred embodiment, and therefore, their explanation is omitted.

Third Preferred Embodiment

FIG. 3 is a view schematically showing a heat recovery system 1 in a third preferred embodiment according to the present invention and showing only differences from the first and second preferred embodiments.

The heat recovery system 1 in the third preferred embodiment also is basically similar to the heat recovery system 1 in the first and second preferred embodiments. Hence, a description will be mainly given of differences between the third preferred embodiment and the first and second preferred embodiments. The same component parts are designated by the same reference numerals.

In the first and second preferred embodiments, the second air cooler 9 and the second oil cooler 11 are connected in series to each other such that the water flows in order to the feedwater tank 5. In contrast, in the present third preferred embodiment, the second air cooler 9 and the second oil cooler 11 are connected in parallel to each other such that water to the feedwater tank 5 is branched to flow in the second air cooler 9 and the second oil cooler 11.

Specifically, the water feed path 22 from the water softener 3 is branched to a first water feed path 29 and a second water feed path 30, wherein the second air cooler 9 is disposed on the first water feed path 29 whereas the second oil cooler 11 is disposed on the second water feed path 30. Although in the preferred embodiment shown in FIG. 3, the feedwater valve 23 is disposed before the branch to the first water feed path 29 and the second water feed path 30, an orifice or a solenoid valve or a motor-operated valve may be formed or disposed in the first water feed path 29 and/or the second water feed path 30. Other constitution and control are similar to those in the first or second preferred embodiment, and therefore, the explanation is omitted below.

Fourth Preferred Embodiment

FIG. 4 is a view schematically showing a heat recovery system 1 in a fourth preferred embodiment according to the present invention.

The heat recovery system 1 in the fourth preferred embodiment also is basically similar to the heat recovery system 1 in each of the preferred embodiments. Hence, a description will be mainly given of differences between the fourth preferred embodiment and the other preferred embodiments. The same component parts are designated by the same reference numerals.

Although the compressor 2 is of an oil lubrication type (i.e., an oil supply type) in each of the preferred embodiments, the compressor 2 is of non-lubrication type (i.e., a dry oil free type) in the fourth preferred embodiment. In this case, the compressor 2 includes a low stage compressor 31 and a high stage compressor 32. Compressed air from the low stage compressor 31 is fed to the high stage compressor 32 through a first inter cooler 33, and the compressed air is further compressed in the high stage compressor 32, to be then fed to the air coolers 9 and 8 as after coolers in sequence.

Moreover, a second inter cooler 34 serving as a heat recovering heat exchanger is disposed on an air feed path from the low stage compressor 31 to the first inter cooler 33. Like the second air cooler 9 and the second oil cooler 11, the feedwater to the feedwater tank 5 is allowed to pass through the second inter cooler 34, and thus, the heat of compression is recovered. At this time, it is an appropriate option how the second inter cooler 34, the second air cooler 9, and the second oil cooler 11 are arranged to allow the feedwater to pass through the feedwater tank 5. For example, the feedwater is allowed to pass through the second inter cooler 34, the second air cooler 9, and the second oil cooler 11 in this order, thus heating the feedwater to the feedwater tank 5.

In the case of the non-lubrication type compressors 31 and 32, there is no lubricant in a compressor body. On the other hand, there is lubricant at a gear unit. The oil may be sometimes cooled. In such a case, a lubricant staying inside of a gear box 35 is fed to the first oil cooler 10 via an oil supply pump 36, and then, is cooled in the first oil cooler 10, before it is returned to the gear unit. The second coil cooler 11 may be disposed on an oil feed path to the first oil cooler 10, like in each of the preferred embodiments.

Also in the present fourth preferred embodiment, like in each of the preferred embodiments, the feedwater to each of the second coolers 34, 9, and 11 or its amount is controlled based on a use load and/or the temperature of hot water after the water passes through each of the second coolers 34, 9, and 11. Other constitution and control are similar to those in each of the preferred embodiments, and therefore, the explanation is omitted below.

Fifth Preferred Embodiment

A heat recovery system 1 in a fifth preferred embodiment also is basically similar to the heat recovery system 1 in the first and second preferred embodiments. Hence, a description will be mainly given of differences between the fifth preferred embodiment and the first and second preferred embodiments. The same component parts are designated by the same reference numerals.

Although the compressor 2 is of the oil lubrication type (i.e., the oil supply type) in the first and second preferred embodiments, the compressor 2 in the fifth preferred embodiment is of a water lubrication type. In this case, the lubricant in the first and second preferred embodiments is replaced with lubricating water. Accordingly, the first oil cooler 10 in the first and second preferred embodiments is replaced with a first water cooler (10) for cooling the lubricating water whereas the second oil cooler 11 in the first and second preferred embodiments is replaced with a second water cooler (11) serving as a heat recovering heat exchanger for heating water by heat of the lubricating water to be fed to the first water cooler (10). Incidentally, in the case of the compressor 2 of the water lubrication type, each of the air coolers 8 and 9 may be omitted.

More specifically, in the case of the water lubrication type compressor 2, compressed air from the compressor 2 is first discharged to a separator (7) (an air-water separator corresponding to the oil separator 7 in the first and second preferred embodiments), where air and water are separated from each other. The compressed air, from which lubricating water is removed in the separator (7), is normally fed to compressed air utilizing equipment not via the air coolers 8 and 9 (i.e., the air coolers 8 and 9 may be omitted) but via the dryer 13, as desired. In contrast, the lubricating water separated from the compressed air in the separator (7) is properly fed to the first water cooler (10), is desirably cooled, and then, is returned to the compressor 2. When the present invention is applied to the water lubrication type compressor 2, the second water cooler (11) is disposed on a water feed path to the first water cooler (10), thereby recovering the heat of compression in the second water cooler (11). Other constitution and control are similar to those in the first and second preferred embodiments, and therefore, the explanation is omitted below.

The heat recovery system 1 according to the present invention may be appropriately varied besides the configuration in each of the preferred embodiments. For example, it is understood that a feedwater pump should be appropriately disposed on the water feed path 22 to the feedwater tank 5 in each of the preferred embodiments. The amount of water which is allowed to pass through the heat recovering heat exchanger (i.e., the second air cooler 9, the second oil cooler 11, or the second inter cooler 34) has been adjusted by adjusting the opening degree of the feedwater valve 23: otherwise, the feedwater pump may be disposed on the water feed path, to be then controlled by an inverter, thus adjusting the flow rate.

Moreover, although the example has been illustrated that the feedwater to the feedwater tank 5 in the boiler 4 is allowed to pass through the heat recovering heat exchanger in each of the preferred embodiments, thereby preheating the feedwater in the boiler 4, the use of the water passing through the heat recovering heat exchanger is not limited to this, and therefore, it may be appropriately varied.

Additionally, in the case of the non-lubrication type compressor as described in the fourth preferred embodiment, the heat of compression becomes high, and therefore, not the hot water but steam may be produced. In other words, the water may be heated to produce steam in the heat recovering heat exchanger (in particular, a heat recovering heat exchanger disposed most downstream). In this case, like the above-described preferred embodiments, the feedwater valve 23 may be controlled based on a water level in a steam producing heat exchanger in place of the control of the feedwater valve 23 based on the temperature of the hot water having passed through the heat recovering heat exchanger. Specifically, the water level of the steam producing heat exchanger is detected, and then, the feedwater to the heat exchanger or its amount may be controlled such that the water level is kept at a set value. At this time, when a steam pressure becomes excessively high inside of the steam producing heat exchanger, the three-way valve 26 (or the three-way valve 28) is switched in the second preferred embodiment (FIG. 2), and thus, cooling is performed by the existing first air cooler 8 (or the first oil cooler 10) on a priority basis.

Furthermore, although the first air cooler 8, the first oil cooler 10, the first inter cooler 33, and the first water cooler (10) have been described in the case of the water cooling type in each of the preferred embodiments, one or two or all of them may be of an air cooling type. In such a case, an air flow by a fan cools the compressed air, the lubricant, or the lubricating water.

In addition, although the second air cooler 9 and the second oil cooler 11 (and further, the second inter cooler 34 in the fourth preferred embodiment) have been disposed in each of the preferred embodiments, all of them need not be disposed but any of them may be omitted, as desired. For example, the second air cooler 9 or the second oil cooler 11 may be omitted in the first or second preferred embodiment.

Additionally, in the case of the non-lubrication type compressor, a compressor may not at all have cooling system for a lubricant. In such a case, a system is configured such that the first oil cooler 10 and the second oil cooler 11 or the oil feed path 14 may be omitted, and further, the heat of compression is recovered in the second air cooler 9 and/or the second inter cooler 34.

Moreover, the number of stages of the compressors 2 may be appropriately varied in each of the preferred embodiments. 

1. A heat recovery system comprising: a first air cooler for cooling compressed air from a compressor; a first oil cooler for cooling a lubricant from the compressor; and a second oil cooler which is disposed on an oil feed path to the first oil cooler and serves as a heat recovering heat exchanger for heating water with the heat of the lubricant to be fed to the first oil cooler.
 2. A heat recovery system according to claim 1, further comprising a second air cooler in addition to the second oil cooler, wherein the second air cooler is disposed on an air feed path to the first air cooler and serves as a heat recovering heat exchanger for heating water with the heat of the compressed air to be fed to the first air cooler, the second air cooler and the second oil cooler being disposed in such a manner as to allow the water to pass therethrough in series or parallel.
 3. A heat recovery system according to claim 1, further comprising a second air cooler in place of the second oil cooler, wherein the second air cooler is disposed on an air feed path to the first air cooler and serves as a heat recovering heat exchanger for heating water with the heat of the compressed air to be fed to the first air cooler.
 4. A heat recovery system according to claim 1, wherein feedwater to the heat recovering heat exchanger or its amount is controlled based on a use load of hot water after passing through the heat recovering heat exchanger.
 5. A heat recovery system according to claim 1, wherein feedwater to the heat recovering heat exchanger or its amount is controlled based on the temperature of hot water after passing through the heat recovering heat exchanger.
 6. A heat recovery system according to claim 1, wherein the compressor is of an oil lubrication type, and includes an oil separator for separating the lubricant from the compressed air discharged from the compressor; and the compressed air, from which the lubricant is separated in the oil separator, is fed to each of the air coolers, whereas the lubricant from the oil separator is fed to each of the oil coolers.
 7. A heat recovery system according to claim 1, wherein the compressor is of a non-lubrication type including a low stage compressor and a high stage compressor, the compressed air from the low stage compressor being fed to the high stage compressor through a first inter cooler, and further compressed in the high stage compressor, before being fed to each of the air coolers as after coolers, and the compressor further includes a second inter cooler which is disposed on an air feed path to the first inter cooler from the low stage compressor and serves as the heat recovering heat exchanger for heating the water with the heat of the compressed air to be fed to the first inter cooler.
 8. A heat recovery system according to claim 7, wherein the water is heated to produce steam in the heat recovering heat exchanger, and feedwater to the heat recovering heat exchanger or its amount is controlled based on the water level of the heat recovering heat exchanger.
 9. A heat recovery system according to claim 1, wherein the compressor is of a water lubrication type, lubricating water being used in place of the lubricant, and accordingly, the first oil cooler being replaced with a first water cooler for cooling the lubricating water whereas the second oil cooler being replaced with a second water cooler serving as a heat recovering heat exchanger for heating water with the heat of the lubricating water to be fed to the first water cooler; and the compressor includes a separator for separating the lubricating water from the compressed air discharged from the compressor; and no first air cooler is disposed, whereby the compressed air from the compressor is discharged via the separator. 